Harvesting‐throughput tradeoff for RF‐powered underlay cognitive radio networks

A green cognitive radio that is solely powered by an energy harvester which extracts energy from the RF signal of a primary user transmitter is considered. The cognitive radio operates in a harvesting–transmitting fashion with the period of one time slot. In each period, it first harvests energy for a fixed duration and then transmits data using the harvested energy for the rest of the period. Considering the intrinsic harvesting‐throughput tradeoff, we optimise the harvesting ratio of the cognitive radio to maximise its achievable throughput, subject to the interference constraint by the primary user receiver. It is shown that the formulated optimisation problem is convex and we derive a closed‐form expression for the optimal harvesting ratio. Simulations validate the correctness and analyse the achievable throughput and optimal harvesting ratio under different parameters.